Anti-neutrophil cytoplasmic autoantibodies (ANCA) have provided unique and important clinical, pathologic and pathogenic insights into a spectrum of systemic necrotizing vasculitides, as well as necrotizing and crescentic glomerulonephritis. ANCA are excellent serologic markers of these diseases, and may be useful indicators of disease activity. The in vitro observation that ANCA cause neutrophil and monocyte activation, and endothelial cell injury suggest that ANCA may be pathogenic. The long term objectives and aims of the proposed research are: 1) to continue to define the relationship between ANCA of various specificities and the clinicopathologic expression of human diseases; 2) to understand the molecular immununology of the ANCA immune response; 3) to determine by in vitro analysis the mechanism of ANCA-induced leukocyte activation, and the interacting factors that cause ANCA-activated leukocytes to injure endothelial cells; and 4) to develop an in vivo model of ANCA-induced disease. The first goal will be achieved by correlating vasculitic syndromes and disease activity with ANCA antigen specificities (at the molecular and epitope level), ANCA isotypes, ANCA titers, and levels of other concomitant autoantibodies. The second aim will be explored by determining the fine specificity of the autoimmune response to ANCA antigens, the clonality of this autoimmune response, and ANCA idiotopes in individual patients and among different patients (including shared idiotopes). The third aim will explore the signal transduction pathways responsible for ANCA-induced leukocyte activation. The factors that cause and modulate ANCA-induced leukocyte-mediated endothelial damage will be determined, and endothelium from different vascular beds will be used to investigate the preferential organ system distribution of different types of ANCA associated disease. The experimental procedures for the fourth aim will use isolated and perfused microcirculatory preparations, and whole animal models to develop an in vivo model of ANCA-induced disease. If an in vivo model of ANCA-induced vasculitis is established, a host of new questions will be unveiled dealing with the pathobiology of this autoimmune disease. If ANCA are proven to cause vasculitis, then a previously unrecognized pathogenic mechanism of vascular inflammation will have been discovered.